The copolymerization of 1,3‐butadiene with styrene by butyllithium initiation

Abstract

Abstract The homopolymerization of styrene (1 M ) by n ‐butyllithium (0.006 M ) in n ‐heptane at 30°C. is approximately six times faster than the homopolymerization of butadiene under the same conditions. In copolymerizations 1 M in each monomer, butadiene is the more reactive comonomer. When 90% of the butadiene monomer has been converted to polymer, more than 80% of the styrene monomer present at the beginning of the reaction still remains. The initial copolymerization rate is the same as that observed in the polymerization of butadiene alone, and about 10 mole‐% styrene is incorporated into the copolymer initially produced. When the butadiene has all reacted a marked increase in polymerization rate is observed. The copolymer reactivity ratios for initial reaction appear to be 7 for butadiene and nearly 0 for styrene. When the copolymerization is carried out in the presence of concentrations of tetrahydrofuran similar to the concentration of butyllithium, increased polymerization rate is observed. Kinetic experiments indicate that the reaction is first‐order with respect to tetrahydrofuran. The amount of 1,2‐addition in the polybutadiene segments of the copolymer increased from the 7% observed in the absence of ether to 15 and 43% as the ratio of (THF)/(BuLi) was varied from 0.4–20. The copolymer initially produced contained 30 mole‐% styrene over this entire range of ether concentrations. The implications of these observations on the polymerization mechanism are discussed.